1. Field of the Invention
The present invention relates to a gain controlling apparatus and a gain controlling method, an information reproducing apparatus having the gain controlling apparatus and an information reproducing method having the gain controlling method, and an information recording apparatus having the gain controlling apparatus and an information recording method having the gain controlling method. More particularly, the present invention relates to a gain controlling apparatus for controlling a gain of a signal used for a reproducing control or a recording control when at least one of an information reproducing operation and an information recording operation is optically carried out from and onto an information recording medium such as an optical disc and the like, and a gain controlling method for controlling it, an information reproducing apparatus having the gain controlling apparatus and an information reproducing method having the gain controlling method, and an information recording apparatus having the gain controlling apparatus and an information recording method having the gain controlling method.
2. Description of the Related Art
Conventionally, if information is optically reproduced or recorded as mentioned above, a light beam, such as a laser light for the reproduction or the record and the like, is irradiated onto an information recording medium such as an optical disc or the like, and then a signal generated by receiving its reflection light is used to usually carry out various controls or reproducing processes or recording processes.
More concretely, the conventional information reproducing apparatus or information recording apparatus has the following configuration. For example, a light reception signal generated by receiving the reflection light is processed to generate a so-called focus error signal (namely, a focus error signal indicative of a deviation in a direction perpendicular to an information recording medium at a focal position of a light beam) or a tracking error signal (namely, a tracking error signal indicative of a deviation in a direction parallel to the information recording medium at a focal point of a light beam). Based on this, the focal point is servo-controlled in the perpendicular or parallel direction to accurately reproduce or record the information.
In this case, the respective servo controls are carried out by optimizing a gain (or a sensibility) in the focus error signal or the tracking error signal in response to a strength of the obtained reflection light. Here, the reason why the gain is optimized is that the extremely high gains of the respective error signals may cause the mechanism of the servo control to oscillate in the worst case. Thus, the servo control cannot be carried out. On the other hand, the extremely low gains may disable the respective error signals to function as the error signals.
Even if the information is reproduced on the basis of a reproduction signal generated by receiving the reflection light (actually, on the basis of a reproduction RF (Radio Frequency) signal corresponding to the information recorded on an information recording medium and the like), it is usual to adjust a gain of the reproduction signal so as to be suitable for the reproducing process.
Here, as an actual example of the above mentioned optical disc, there is an optical disc which allows recording or reproducing operations for a plurality of times and which is so-called as a CD-RW (Compact Disc-Rewritable), in addition to a conventional CD.
However, according to the above mentioned CD-RW, the intensity of the reflection light, which is obtained by irradiating a light beam onto the CD-RW, is much lower than (e.g., about 12 dB lower than) that of the conventional CD.
Therefore, if it is tried to reproduce the CD-RW by using a conventional information reproducing apparatus for the conventional CD or to record the information onto the CD-RW by using the conventional information recording apparatus, a light reception signal (i.e., a light reception signal obtained by receiving the reflection light from the CD-RW), which has an enough level for the various servo controls as aforementioned, cannot be obtained. This result in that the information cannot be recorded onto the CD-RW, or the information cannot be reproduced from the CD-RW, which is a problem.